Perforation sealer



April 1968 B. T. WILLMAN ETAL 3,376,934

PERFORATI ON SEALER Filed Nov. 19, 1965 FIR-2 ELL ATTORNEY United States Patent 3,376,934 PERFORATION SEALER Bertram T. Willman, New York, N.Y., and James F. McPhail, Houston, Tex., assignors to Esso Production Research Company, a corporation of Delaware Filed Nov. 19, 1965, Ser. No. 508,814 6 Claims. (Cl. 166-193) ABSTRACT OF THE DISCLOSURE The present invention relates to an improved perforation sealer for use in oil wells, gas wells and similar boreholes.

Hydraulic fracturing techniques, well stimulation procedures and other workover operations carried out in oil wells and similar boreholes often require the temporary sealing of perforations through which fluids tend to escape from the tubing or casing. This is normally done by means of ball sealers injected with the treating fluid. These sealers are usually neophrene-coated nylon spheres slightly larger than the nominal size of the perforations. The spheres are carried into the perforations by the escaping fluid and, once seated, tend to prevent further fluid losses. Such sealers are seldom wholly effective. Most wells are per-v forated with tools which may produce elongated holes or cause the tubing or casing to split or crack in the vicinity of the hole, particularly where the tubing or casing is not firmly supported by a cement sheath or a competent formation. Ball sealers of conventional design do not effectively seal such splits, cracks or other irregular openings.

The present invention provides an improved sealer which effectively closes off irregular perforations and prevents the escape of fluids through them. The improved sealer includes an at least partially spheroidal body of resilient material of suflicient size to lodge in a perforation as fluid enters the perforation and a flexible skirt of fluid-impervious material attached to and extending outwardly about the body a distance suflicient to overspread the wall surface adjacent the perforation. When such a sealer seats in a non-circular perforation, the escape of fluid through the unplugged portion of the perforation around the sealer body forces the flexible skirt into or over the opening. This seals the irregular opening and thus reduces or prevents further escape of the fluid. When the pressure within the pipe is reduced and the well is placed on production, the sealer is dislodged and carried to the surface with the produced fluid. The device thus permits more effective temporary sealing of the perforations than can ordinarily be obtained with ball sealers of conventional design.

The nature and objects of the invention can best be understood by referring to the following detailed description of the improved sealer and to the accompanying drawing in which:

FIGURE 1 is a vertical elevation, partially in section, of a perforated pipe string showing use of the sealers to plug irregular perforations; and

FIGURE 2 is a sectional view of an alternate embodiment of the improved sealer.

The pipe string 11 shown in FIGURE 1 of the drawing is a string of easing which has been installed in a Well and cemented in place in the conventional manner. The cement behind the casing and the adjacent subterranean formation are not shown. A conventional explosive jet or gun-type perforator has been employed to perforate the casing at points 12, 13 and 14. In each case the perforator has split or cracked the casing around the perforation so that the resultant openings in the casing are noncircular. The splits or cracks are indiacted by reference numerals 15, 16 and '17. These noncircular openings prevent the effective use of conventional ball sealers for plugging the perforations.

The improved perforation sealer shown in FIGURE 1 includes an at least partially spheroidal body of resilient material 18 of sufficient size to lodge in a perforation and is provided with a flexible, fluid-impervious skirt 19 which is attached to and extends from the body a distance suificient to overspread the wall surface adjacent the perforation. The body 18 may be formed. of neophrenecoated nylon, polypropylene, polyethylene, polyisobutylene, polybutadiene or a similar polymeric material, synthetic rubber or resin. The material employed should be resistant to hydrocarbons if the sealer is' to be used in an oil environment. Ordinarily, the density of the material should be greater than that of the fluid in which the sealer is to be used. Alternatively, the body should be weighted so that it will sink in the fluid within the wellbore. The diameter should be suflicient to permit lodging of the body within the perforation and prevent its being extruded under high differential pressures. Most perforations are about one-half inch in diameter and hence a ball or similar body about five-eighths or three-quarters-of an inch in diameter will ordinarily be employed. For larger perforations, a correspondingly larger ball or similar body will be required.

As can be seen from the cross sectional view of the sealer lodged in perforation 12 of FIGURE 1 body 18 vmay be made in two pieces which are later joined by means of a suitable adhesive or with a rivet or similar metallic fastener 20. The use of a rivet or the like having an enlarged head provides a convenient method for joining the two pieces and at the same time weighting the body so that it will sink in the fluid in the wellbore at the desired rate. This rate will normally fall in the range between about one-half to about ten feet per second but may be somewhat lower if desired. The amount of weight required to achieve such a rate will depend, of course, upon the density and viscosity of the fluid in the wellbore, the density of the material from which the sealer is made, and the configuration of the sealer.

The skirt 19 of the sealer shown in FIGURE 1 is made of rubberized fabric, plastic, synthetic rubber or a similar flexible, fluid-impervious material. It is generally preferred that the skirt consist of multiple overlapping strips of sheet rubber or similar material which will readily be carried into the cracks or splits surrounding the perforation as shown in FIGURE 1. In some cases, however, a single piece of suitable sheet material provided with folds or pleats may be used. In either case, the skirt may be mounted between the two body sections and secured with an adhesive or by means of a rivet or similar member 20. The density of the material in the skirt should generally be less than that of body 18 so that the skirt will trail behind as the sealer drops through the fluid in the tubing or casing. The length or radius of the skirt will normally be from about two to about six times the diameter of the sealer body but may be greater if desired.

FIGURE 2 of the drawing depicts an alternate embodiment of the sealer in which the body includes a hemispherical lower section 21 and a flat circular upper section 22. The multiple overlapping strips 23 of the skirt are held in place between these two members by rivet 24. As the sealer drops through the fluid in the tubing or casing, the strips trail behind the body member as depicted. The use of a body composed of a hemispherical member and a disc as thus shown in FIGURE 2 is advantageous in that the disc will contact the wall of the tubing or casing as the sealer approaches the perforation and help direct the lower hemispherical section 21 into the perforation. The embodiment of FIGURE 2 may be made of materials similar to those referred to in connection with FIGURE 1 of the drawing.

The improved sealer of the invention is used in much the same way that conventional ball sealers are employed. When the necessity for plugging the perforations in a string of tubing or casing containing fluid arises during a workover job or similar operation, the sealers are dropped into the fluid at the wellhead. As each sealer settles through the fluid, the skirt trails behind the body as shown. On approaching a perforation through which fluid is escaping, the sealer body is carried into the perforation. The flexible skirt attached to the body is then forced into any splits, cracks or other irregularities adjacent the body section by the escaping fluid. Due to the overlapping of the strips and generally small width of the cracks, a seal capable of withstanding high pressures without rupturing can be readily obtained, particularly where the fabric or other material seats in contact with the cement or formation adjacent the outer wall of the pipe string. The use of an elastic material capable of stretching in two different directions minimizes tearing within the crack or split. The perforations in the upper part of the string or casing are normally sealed first and the sealers then seat in progressively lower perforations. In cases where some perforations are not taking fluid because of low permeability, however, the sealers will preferentially seat in the perforations communicating with high permeability zones into which fluid flow rates are highest. This makes the use of sealers for increasing differential pressure into the less permeable Zones advantageous. When it becomes necessary to remove the sealers and restore communication, the pressure is reduced in the wellbore and fluid is back flowed into the casing or tubing through the perforations. This dislodges the sealers from the perforations and adjacent splits, cracks or other 4 irregular openings. The sealers can then be circulated to the surface with the produced fluids.

What is claimed is:

1. A ball sealer for plugging a perforation in the wall of a pipe string in an oil well or similar borehole comprising an at least partially spheroidal body of suflicient size to lodge in said perforation in the wall of said pipe string as fluid carrying said body flows into the perforation and a skirt of a flexible, fluid-impervious material attached to and extending from said body a distance sufficient to overspread the wall surface adjacent the perforation, said body including two immediately adjacent portions between which said skirt is sandwiched.

2. A sealer as defined by claim 1 wherein said skirt is composed of multiple overlapping strips of said flexible, fluid-impervious material.

3. A sealer as defined by claim 1 wherein the adjacent portions of said body comprise a substantially hemispherical member and a flat circular member having a greater diameter than said substantially hemispherical member, the base of said substantially hemispherical member being adjoined to the face of said circular memher.

4. A sealer as defined by claim 1 wherein the adjacent portions of said body are composed of at least two members held together be a metallic fastener.

5. A sealer as defined by claim 1 wherein said body is composed at least in part of a resilient polymeric material.

6. A sealer as defined by claim 1 wherein the length of said skirt is from about two to about six times the diameter of said body.

References Cited UNITED STATES PATENTS 1,606,206 11/1926 Boynton 166-193 2,253,224 8/1941 Bleakley 166192 2,646,845 7/1953 Schillinger 166-192 X 2,651,367 9/1953 Baker 166194 2,754,910 7/1956 Derrick 166--193 X 3,032,115 5/1962 Smith 166-192 X 3,054,455 9/1962 Keltner 166192 X CHARLES E. OCONNELL, Primary Examiner.

NILE C. BYERS, IR., Examiner. 

